Electrodeposited foil with controlled properties for printed circuit board applications and procedures and electrolyte bath solutions for preparing the same

ABSTRACT

Copper conductive foil for use in preparing printed circuit boards is electrodeposited from an electrolyte solution containing copper ions, sulphate ions, animal glue and thiourea. The thiourea operates to decrease the roughness of the foil, to enable operation at higher current densities and/or to modify the ductility characteristics of the foil.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to etchable copper conductive foils usefulfor preparing printed circuit boards and particularly toelectrodeposition procedures and electrolyte bath solutions forcontrolling the properties of such foils. More specifically theinvention relates to procedures and electrolyte bath solutions usefulfor controlling foil properties such as roughness, elongation, tensilestrength and ductility. By controlling these properties theelectrodeposition operation may be conducted with greater efficiency.

2. Description of the Prior Art

Printed circuit board (PCB) components have become widely used in avariety of applications for radios, televisions, computers, etc. Ofparticular interest are multi-layer PCB laminates which have beendeveloped to meet the demand for miniaturization of electroniccomponents and the need for PCBs having a high density of electricalinterconnections and circuitry. In the manufacture of PCBs, rawmaterials, including conductive foils, which are usually copper foils,and dielectric supports comprising organic resins and suitablereinforcements, are packaged together and processed under temperatureand pressure conditions to produce products known as laminates. Thelaminates are then used in the manufacture of PCBs. In this endeavor thelaminates are processed by etching away portions of the conductive foilfrom the laminate surface to leave a distinct pattern of conductivelines and formed elements on the surface of the etched laminate.Laminates and/or laminate materials may then be packaged together withetched products to form multi-layer circuit board packages. Additionalprocessing, such as hole drilling and component attaching, willeventually complete the PCB product.

With multiple-layer circuit boards, it may be appreciated thatvariations in the thickness of the copper foil will lead tononuniformities of transmission line characteristics within the foil andresult in unpredictable electrical characteristics for any given PCB. Asthe integrated circuits increase in speed, the problem becomes moreserious. The dielectric constant and thickness of the substrate alongwith the height, width, spacing and length of the conductive tracesdetermine many of the electrical performance characteristics of the PCB.

The PCB industry's push toward miniaturization and increased performanceper package is resulting in conductors of ever smaller widths, moreclosely spaced on thinner substrates. The increase in switchingfrequency of solid state electronic devices that are interconnected bythe copper traces, results in further demands on the PCB due to the"skin effect" which results during high frequency operation along aconductor. The characteristics of the copper foil have a significanteffect on the electrical performance of the finished PCB. Themetallurgical properties of the copper foil are also important in thePCB production process. For example, a foil used in multi-layerlaminates must not crack during hole drilling. Also, foils which areless susceptible to wrinkling during the lamination process arepreferable for reducing scrap losses.

The production of copper foil by electrodeposition processes involvesthe use of an electroforming cell (EFC) consisting of an anode and acathode, an electrolyte bath solution, generally containing coppersulphate and sulphuric acid, and a source of current at a suitablepotential. When voltage is applied between the anode and cathode, copperdeposits on the cathode surface.

The process begins by forming the electrolyte solution, generally bydissolving (or digesting) a metallic copper feed stock in sulphuricacid. After the copper is dissolved the solution is subjected to anintensive purification process to ensure that the electrodeposited foilcontains no disruptions and/or discontinuities. Various agents forcontrolling the properties may be added to the solution.

The solution is pumped into the EFC and when voltage is applied betweenthe anode and cathode, electrodeposition of copper occurs at thecathode. Typically, the process involves the use of rotatablecylindrical cathodes (drums) that may be of various diameters andwidths. The electrodeposited foil is then removed from the cylindricalcathode as a continuous web as the cathode rotates. The anodes typicallyare configured to conform to the shape of the cathode so that theseparation or gap therebetween is constant. This is desirable in orderto produce a foil having a consistent thickness across the web. Copperfoils prepared using such conventional electrodeposition methodologyhave a smooth shiny (drum) side and a rough or matte (copper depositgrowth front) side. Conventionally such foils are bonded to dielectricsubstrates to provide dimensional and structural stability thereto, andin this regard, it is conventional to bond the matte side of theelectrodeposited foil to the substrate so that the shiny side of thefoil faces outwardly from the laminate. In a commercial sense, usefuldielectric substrates may be prepared by impregnating woven glassreinforcement materials with partially cured resins, usually epoxyresins. Such dielectric substrates are commonly referred to as prepregs.

In preparing laminates, it is conventional for both the prepreg materialand the electrodeposited copper foil material to be provided in the formof long webs of material rolled up in rolls. The rolled materials aredrawn off the rolls and cut into rectangular sheets. The rectangularsheets are then laid-up or assembled in stacks of assemblages. Eachassemblage may comprise a prepreg sheet with a sheet of foil on eitherside thereof, and in each instance, the matte side of the copper foilsheet is positioned adjacent the prepreg so that the shiny sides of thesheets of foil face outwardly on each side of the assemblage.

The assemblage may be subjected to conventional laminating temperaturesand pressures between the plates of laminating presses to preparelaminates comprising sandwiches of a sheet of prepreg between sheets ofcopper foil.

The prepregs used conventionally in the art may consist of a woven glassreinforcement fabric impregnated with a partially cured two-stage resin.By application of heat and pressure, the matte side of the copper foilis pressed tightly against the prepreg and the temperature to which theassemblage is subjected activates the resin to cause curing, that iscross linking of the resin and thus tight bonding of the foil to theprepreg dielectric substrate. Generally speaking, the laminatingoperation will involve pressures in the range of from about 250 to about750 psi, temperature in the range of from about 350° to 450° F. and alaminating cycle of from about 40 minutes to about 2 hours. The finishedlaminate may then be utilized to prepare PCBs.

Conductive foils for PCB applications are conventionally treated, atleast on the matte side, for enhanced bonding and peel strength betweenthe matte side and the laminate Typically the foil treatment involvestreatment with a bonding material to increase surface area and thusenhance bonding and increase peel strength. The foil may also be treatedto provide a thermal barrier, which may be brass, to prevent peelstrength from decreasing with temperature. Finally, the foil may betreated with a stabilizer to prevent oxidation of the foil. Thesetreatments are well known and further description thereof is notnecessary at this point.

A number of manufacturing methods are available for preparing PCBs fromlaminates. Additionally, there is a myriad of possible end useapplications. These methods and end uses are known and need not bediscussed in detail here. But suffice it to say that each method andeach end use has its own set of idiosyncracies which often may dictatethe physical and/or chemical characteristics of the foil itself. Thus,the industry has established a set of definitions and has defined eightseparate categories or classes of copper foil. These definitions and thecharacteristics of each of the eight classes of foil are set out in apublication of the Institute for Interconnecting and PackagingElectronic Circuits (IPC) entitled "Copper Foil for Printed WiringApplications" and designated IPC-CF-150X.

The document IPC-CF-150X, where X denotes, in alphabetical order, thevarious revisions, contains the specifications for the acceptabletechnical properties and performance of copper foils for the manufactureof printed circuits. This document in its entirety is contained inmilitary specification MIL-P-13949 for polymeric dielectric laminatesand bonding sheets to be used in the production of printed circuitboards. Therefore, certification of foils to the IPC-CF-150X standardsautomatically ensures qualification to military specification standards.

The current IPC publication is Revision E published May, 1981 anddesignated IPC-CF-150E and this publication is hereby specificallyincorporated herein by reference.

IPC-CF-150E sets forth the following table which defines the minimumvalues for certain mechanical properties for each class of foil

                                      TABLE 1                                     __________________________________________________________________________    Mechanical Properties (Minimum Values)                                        (The copper foil shall conform to the tensile and elongation                  requirements                                                                  when tested in both longitudinal and transverse directions.)                                                              AT ELEVATED                                    AT ROOM TEMPERATURE 23° C.                                                                            TEMPERATURE 180° C.            Copper                % DUCTILITY                   % Elongation              Type                                                                              Copper**                                                                           Tensile Strength                                                                           Elong. (2.0" G.L.)                                                                              Tensile Strength                                                                          (2.0" G.L.)               and Weight     Mega Pascals                                                                         CHS       Fatigue      Mega Pascals                                                                         CHS                       Class                                                                             oz.  Lbs./In..sup.2                                                                      (MPa)  2"/Minute Ductility                                                                             Lbs./In..sup.2                                                                     (MPa)  0.05"/Minute          __________________________________________________________________________    TYPE                                                                              1   1/2  15,000                                                                              103.35 2.0       Not developed                                                                         NOT APPLICABLE                    E       1    30,000                                                                              206.70 3.0                                                         2+   30,000                                                                              206.70 3.0                                                     2   1/2  15,000                                                                              103.35 5.0       Not developed                                                                         NOT APPLICABLE                            1    30,000                                                                              206.70 10.0                                                        2+   30,000                                                                              206.70 15.0                                                    3   1/2  15,000                                                                              103.35 2.0       Not developed                                                                         --    --    --                            1    30,000                                                                              206.70 3.0               20,000                                                                             137.80 2.0                           2+   30,000                                                                              206.70 3.0               25,000                                                                             172.25 3.0                       4   --   --    --     --        Not developed                                                                         --   --     --                            1    20,000                                                                              137.80 10.0              15,000                                                                             103.35 4.0                           2+   20,000                                                                              137.80 15.0              15,000                                                                             103.35 8.0                   TYPE                                                                              5   1/2  50,000                                                                              344.50 0.5       30.0    --   --     --                    W       1    50,000                                                                              344.50 0.5               20,000                                                                             137.80 2.0                           2+   50,000                                                                              344.50 1.0               40,000                                                                             375.60 3.0                       6   1    25,000 to                                                                           172.25 to                                                                            1.0 to    30.0 to NOT APPLICABLE                                 50,000*                                                                             344.50 20.0      65.0                                              2+   according                                                                           according to                                                                         according to                                                                            according to                                           to temper                                                                           temper temper    temper                                        7   1/2  15,000                                                                              103.35 5.0       65.0    --   --     --                            1    20,000                                                                              137.80 10.0              14,000                                                                              96.46 6.0                           2+   25,000                                                                              172.25 20.0              22,000                                                                             151.58 11.0                      *   1/2  15,000                                                                              103.35 5.0       25.0    NOT APPLICABLE                        8   1    20,000                                                                              137.80 10.0                                                __________________________________________________________________________     *Properties given are following a time/temperature exposure of 15 minutes     at 177° C. (350° F.).                                           **Minimum properties for testing copper weights less than 1/2 ounce shall     be agreed to between user and vendor.                                    

Of the classes of foil defined by IPC-CF-150E, perhaps the most widelyused by the industry is IPC Class 1 which is sometimes referred tosimply as standard foil. IPC Class 1 foil is an electrodeposited foilthat has a generally acceptable room temperature ductilitycharacteristics Another class of foil that is widely used by theindustry is IPC Class 3 foil which is also sometimes referred to as highelevated temperature ductility foil. IPC Class 3 foil is anelectrodeposited foil that has high ductility at elevated temperaturesand thus is able to withstand the stresses and strains imposedparticularly at thru holes by differential thermal expansion duringsoldering operations and in high temperature use applications.

Copper foils have been produced for PCB use by two major methods,rolling or electrodeposition. The invention of the present applicationrelates to the latter. As set forth above, to produce copper foil byelectrodeposition, a voltage is imposed between an anode and a cathodeimmersed in a copper containing electrolytic bath solution. Copper iselectrodeposited on the cathode in the form of a thin metal film. Thequalities and characteristics of the metal film are a function of manyparameters such as current density, temperature, substrate material,solution agitation and electrolyte solution composition. Additives areoften placed in the electrolyte solution so that the electrodeposit maybe formed with certain desired qualities, a main one of which is acertain controlled roughness. Without the presence of additives thecopper deposits have the tendency, as a result of crystallineimperfections and grain boundaries, to grow with an uncontrolledroughness that is not uniform. Additionally, a certain controlled degreeof roughness is often desired by the copper foil user so that the bondstrength is increased between the copper foil and the dielectric supportto which the copper foil is adhered, and the copper foil. Roughnesscontributes to the strength of the bond by increasing the surface areaavailable for bonding.

A gelatine component may often be included in the electrolyte solutionto control roughness. The gelatine component most commonly used isanimal glue. Glue is believed to function by adsorbing onto theelectroplating surface to thus decrease the exchange current density forcopper deposition, a condition found in the theories ofelectrodeposition to be favorable to production of smoother deposits.

According to known methodology, copper foil may be electrodeposited froman electrolyte solution containing about 100 grams per liter (g/l) ofcopper, about 80 g/l of sulphuric acid and about 80 parts per million(ppm) of chloride ions. Glue may be added to the solution duringelectrodeposition at addition rates ranging from about 1/2 milligram ofglue per minute per 1,000 amperes (mg/min.kA) up to about 11 mg/min kA.The process generally was conducted at a temperature of about 60 degreescentigrade (°C.) using a current density between about 200 and about1,400 amperes per square foot (ASF). It has been determined that theroughness of the matte surface of the deposited copper foil generallyincreases as the glue addition rate is decreased and/or the currentdensity is increased. Electrolyte flow is maintained so that platingoccurs below the mass transfer limited current density. In such processthe glue addition rate may be varied to vary the metallurgicalproperties of the copper foil to meet various performance criteria.Typical matte side roughnesses (R_(tm)) of copper foils produced by thismethod, as measured on a Surftronic 3 profilometer (Rank Taylor HobsonLtd.--Leicester, England), range from about 4.75 μm to about 8 μm for1/2 oz. copper foil; from about 6.5 μm to about 10 μm for 1 oz copperfoil; and from about 8.75 μm to about 15 μm for 2 oz. copper foil. IPCClass 1 foils were produced by this method at glue addition ratesbetween 5 and 11 mg/min kA while IPC Class 3 foils were produced at glueaddition rates less than 5 mg/min.kA. Low profile (low roughness) foilscould be produced by increasing the glue addition rate to above 11mg/min kA.

One disadvantage of the known method is that as the copper foil isdeposited to greater thicknesses, the roughness increases and the numberof isolated roughness elements also increases. The isolated roughnesselements may be separated by interspersed smooth areas, rendering thecopper foil unusable for some critical electronic applications. Tominimize such roughness increases, the current must be decreased,resulting in lost production capacity. Another disadvantage of the knownmethodology is that copper foils with lower matte side roughnesses (lowprofile foils) were not readily obtainable without correspondingdecreases in metallurgical qualities, such as in elevated temperatureelongation Thus, low profile IPC Class 3 foils generally could not beproduced by the known methods without substantial loss of efficiency. Inthis regard, the lowest R_(tm) achievable using known methods forproducing IPC Class 3 foils was approximately 11 to 12 μm for 2 oz.foil, approximately 7 to 8 μm for 1 oz. foil, and approximately 5 to 6μm for 1/2 oz. foil. Furthermore, the lowest R_(tm) achievable using theknown methods for producing Class 1 foils was approximately 5.2 μm for 2oz. foil, about 5 μm for 1 oz. foil, and about 4.6 μm for 1/2 oz. foil.On the other hand, low profile foils having a R_(tm) below about 4.5 μmhave sometimes become desirable because they provide finer linedefinition, better impedance control and reduced propagation delays. Inparticular low profile foils are desirably used to facilitate tapeautomated bonding operations. In general, low roughness facilitates theuse of less resin in bonding the foil to a dielectric substrate as wellas the use of thinner laminates.

The prior art processes described above and which have utilized glue inan attempt to control properties such as roughness and ductility, havesuffered from several distinct and difficult disadvantages. Firstly,when the process was used to make standard IPC Class 1 foils, theoverall efficiency of the process was limited by the fact that increasesin current density (ASF) were generally accompanied by increases inroughness and decreases in ductility. Secondly, to decrease roughnessand produce low profile foils it was necessary to increase the glueaddition rate; however, an increased glue addition rate resulted indecreased ductility. So it was necessary to reduce the current densityto counteract the loss of ductility. Finally, to produce a suitable IPCClass 3 foil it was necessary to decrease the glue addition rate, butthis caused an increase in roughness. So in this case it was alsonecessary to reduce the current density to counteract the increasedroughness.

It was generally known in the copper electrorefining industry thatsurface active agents could be used to produce bulk copper cathodeshaving smoother surfaces. The smoother surfaces are desirable in therefining industry from the standpoint of plant efficiency. The coppercathodes in a refining plant are deposited to substantial thicknesses,i.e., many millimeters. As the deposit grows to such thicknesses, thecathode becomes rougher, and in extreme cases, dendrites and nodulesform on the cathodes causing shorts in the cells. When such shortingoccurs plating ceases. To maintain the plating output, the cathode mustbe changed before a short occurs. In order to minimize the number ofcathode changes and to deposit a greater thickness of copper for eachcathode, the electrorefining industry has used addition agents such asanimal glue, chloride ion and thiourea to reduce dendrite and noduleformation on the copper cathodes.

The electrorefining industry has sought to prepare higher quality coppercathodes, for instance, for use as raw material in super-fine copperwire. E. H. Chia et al., "Organic Additives: A Source of Hydrogen inCopper Cathodes," Journal of Metals, April, 1987, pages 42-45. Chia etal. discuss the use of organic additives including combinations ofthiourea and glue, in electrorefining copper. Chia et al. specificallyaddress the assumption that thiourea contributes hydrogen at the cathodein the refining tank.

S. E. Afifi et al., "Additive Behavior in Copper Electrorefining,"Journal of Metals, February, 1987, pages 38-41, also discuss the use oforganic additives such as gelatine and thiourea in electrodepositionprocesses. This paper states that such additives can be used to modifythe crystal size of the deposit to improve the brightness of thedeposit. The authors conclude that small concentrations of thiourea actbeneficially toward surface brightness of deposits up to very highvalues of current densities, but at higher concentrations of thioureathe surface brightness of deposits decreases rapidly, possibly due toincreased precipitation of cupric sulfide or sulphur on the electrodesurfaces.

Knuutila et al. "The Effect of Organic Additives on theElectrocrystallization of Copper," The Electrorefining of Copper,examine the behavior of thiourea, animal glue and chloride ions in theelectrolysis of copper. This paper deals with changes in polarizationcurves in the electrolysis of copper and indicates that themicrostructure of a copper cathode obtained from an electrolytecontaining thiourea differs drastically from the microstructure obtainedfrom a bath containing only glue. Specifically, the thioureafield-oriented structure is evident, and the grain size is much finer.Furthermore, animal glue provides a microstructure in deposited copperhaving a basis-oriented structure.

Ibl et al., "Note on the Electrodeposits Obtained at the LimitingCurrent," Electrochimica Acta, 1972, Vol. 17, pages 733-739, disclosethe use of thiourea in acid cupric sulfate solutions as a levelingagent.

Franklin, "Some Mechanisms of Action of Additives in ElectrodepositionProcesses," Surface and Coatings Technology, Vol. 30, pages 415-428,1987, discusses the use of a number of additives in electrodepositionprocesses, including one for copper.

While the surface deposit effects of glue and thiourea are thus wellknown to those skilled in the art of copper electrorefining to producethick copper deposits, the use of thiourea has not previously beenapplied in the copper foil industry for controlling process parametersor properties such as surface roughness, tensile strength, elongationand/or ductility of thin copper foils to be used in the PCB industry.

SUMMARY OF THE INVENTION

The present invention addresses the problems outlined above by providingan improvement for the existing electrolytic processes used for formingcopper foils for printed circuit board applications. The invention isapplicable in connection with processes for electrically forming suchcopper foils wherein an electrical current is applied between an anodeand a cathode in an electrolyte solution containing copper ions, sulfateions and a gelatine component to cause electrodeposition of copper foilat the cathode. The improvement for such process provided by theinvention comprises incorporating into the solution an electrodepositedfoil characteristics controlling quantity of an active sulphurcontaining component. In one sense of the invention the quantity of suchactive sulphur containing component may be sufficient for decreasing theroughness of the electrodeposited foil. In another sense of theinvention the amount of the active sulphur containing component may besufficient for increasing the tensile strength of the electrodepositedfoil. In yet another sense of the invention the amount of active sulphurcontaining component may be sufficient to enable increase of the currentapplied between the anode and the cathode without altering the basiccharacteristics of the foil.

A very important aspect of the invention is that the process providedthereby is capable of achieving production of IPC Class 3 foil having aroughness which is less than that which has been achievable utilizingprior art processes. Additionally, the invention facilitates productionof IPC Class 3 foil at higher current densities than have heretoforebeen achievable.

In accordance with a particular embodiment of the invention the gelatinecomponent may comprise animal glue. In another important embodiment theactive sulphur containing component may comprise thiourea. And in apreferred aspect of the invention the animal glue may be added to theelectrolyte solution at a rate in the range of from about 0.2 mg/min.kAto about 20 mg/min.kA and the thiourea may be added to the electrolytesolution at a rate in the range of from about 1.25 mg/min.kA to about 50mg/min.kA.

The invention thus provides a process for preparing a low profile copperfoil for printed circuit board applications comprising preparing acopper electrodeposition bath solution containing copper ions, sulphateions, a gelatine component and a roughness decreasing quantity of anactive sulphur containing component, and then cathodically platingcopper from the bath solution to provide a foil having a thicknesssuitable for printed circuit board applications. Again, the activesulphur containing component may be preferably be thiourea.

In another important aspect the invention provides an electrolytic bathfor electrodepositing copper foil for printed circuit board applicationscomprising an aqueous solution containing copper ions, sulphate ions agelatine component and a roughness decreasing quantity of an activesulphur containing component. In a preferred aspect of the invention theactive sulphur containing component may be thiourea and the quantity ofthiourea present in the bath may range from about 0.28 ppm to about 11.1ppm.

The invention also provides an electrolytic bath for electrodepositingcopper foil having increased resistance to wrinkling for printed circuitboard applications. In this aspect of the invention the bath maycomprise an aqueous solution containing copper ions, sulphate ions, agelatine component and a tensile strength increasing quantity of anactive sulphur containing component. The invention also provides aprocess for preparing a low profile copper foil for printed circuitboard applications utilizing a copper electrodeposition bath solutioncontaining copper ions, sulphate ions, a gelatine component and atensile strength increasing quantity of an active sulphur containingcomponent.

In another important aspect the invention provides a process forpreparing an electrodeposited copper foil for printed circuit boardapplications and having IPC-CF-150E Class 1 or Class 3 properties. Inthis aspect of the invention the process includes the steps of preparinga copper electrodeposition bath solution comprising copper ions,sulphate ions and gelatine, applying an electrical current to the bathsolution to cathodically plate copper therefrom, and including aroughness decreasing quantity of an active sulphur containing componentin the solution to thereby facilitate a corresponding increase in theelectrical current density.

The invention also provides a process for preparing an electrodepositedcopper foil for printed circuit board applications and havingIPC-CF-150E Class 1 properties and increased resistance to wrinkling. Inthis form of the invention the process includes the steps of preparing acopper deposition bath solution comprising copper ions, sulphate ionsand gelatine, applying an electrical current to the solution tocathodically plate copper from the solution, and including a tensilestrength increasing quantity of an active sulphur containing componentin the solution.

The invention also provides an electrolytic bath for electrodepositinglow profile copper for printed circuit board applications comprising anaqueous solution containing a gelatine component and a roughnessdecreasing quantity of an active sulphur containing component. In thisembodiment of the invention the electrolytic bath may comprise an acidsolution of copper sulfate and sulphuric acid. Additionally, the sulphurcontaining component may comprise thiourea and the gelatine componentmay comprise animal glue. The thiourea may be present in the bathsolution in an amount ranging from about 0.28 ppm to about 11.1 ppm andthe animal glue may be present in the solution in an amount ranging fromabout 0.044 ppm to 4.4 ppm.

The invention also provides a 2 oz. copper foil for printed circuitboard applications having IPC-CF-150E Class 1 properties and an R_(tm)of less than about 8.0 μm. Additionally, the invention provides a 1 oz.copper foil for printed circuit board applications having IPC-CF-150EClass properties and an R_(tm) of less than about 5 μm. Further theinvention provides a 1/2 oz. copper foil for printed circuit boardapplications having IPC-CF-150E Class 1 properties and an R_(tm) of lessthan about 4.6 μm. The invention also provides low profile copper foilfor printed circuit board applications having IPC-CF-150E Class 3properties. In this regard, the invention provides a 2 oz. copper foilfor printed circuit board applications having IPC-CF-150E Class 3properties and an R_(tm) of less than about 11 μm, a 1 oz. copper foilfor printed circuit board applications having IPC-CF-150E Classproperties and an R_(tm) of less than about 7 μm, and a 1/2 oz. copperfoil for printed circuit board applications having IPC-CF-150E Class 3properties and an R_(tm) of less than about 5 μm.

In a broader respect the invention provides an electrodeposited copperfoil having a uniform controlled roughness and/or improved metallurgicalproperties. In accordance with the invention such copper foil may beproduced at higher current densities than are achievable using presenttechnology The invention provides methodology for electrolyticallydepositing copper foils having high elevated temperature elongation aswell as low profile.

In sum the invention provides the methodology for producing low profilefoils without a concomitant decrease in the elongation of the foil.Thus, the low profile copper foil may be produced without acorresponding reduction in current density in the electrolytic cell.Additionally, in accordance with the invention standard foil productsmay be produced at increased current densities without experiencingincreased roughness This also facilitates the production of foilproducts having increased tensile strength and thus enhanced resistanceto wrinkling. Finally, the invention provides the methodology for makingIPC Class 3 foils at higher current densities as a result of theincorporation of a roughness decreasing quantity of the active sulphurcontaining component in the electrolytic bath.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow diagram illustrating an electroforming celloperable in accordance with the principles and concepts of theinvention;

FIG. 2 is a bar graph setting forth data to illustrate benefits achievedthrough the use of the invention; and

FIG. 3A, 3B, 3C and 3D are microphotographs illustrating thecross-sectional configurations of foils produced in accordance with theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a method for manufacturing copper foilproducts by electrodeposition wherein a number of important physicalproperties and characteristics of the foil may be closely controlled. Inparticular the invention provides for the electrodeposition of copperfoil by cathodic electrodeposition from an electrolyte solutioncontaining copper ions, sulphate ions and a gelatine component and towhich is added a copper foil characteristics controlling quantity of anactive sulphur containing component. The inclusion of the active sulphurcontaining component, which preferably may be thiourea or some othercomponent having a bivalent sulphur atom, both bonds of which aredirectly connected to a carbon atom together with one or more nitrogenatoms also directly connected to the carbon atom, provides a mechanismfor achieving close control of certain critical characteristics of theelectrodepositing foil during the conduct of the electrodepositingoperation. By adding such component to the electrolyte solutioncontaining a gelatine component, the roughness, elongation and tensilestrength of copper foil may each be manipulated and controlled. As aresult it is often also possible to achieve an increase in currentdensity.

An electroplating operation conducting in accordance with the inventionmay be carried out in a continuous electroplating system of the sortdepicted schematically in FIG. 1 of the drawings. The system includes anelectroforming cell (EFC) 10 that comprises an anode 12, a cathode 14, avessel 16 and an electrolyte solution 18 contained in vessel 16 and inwhich anode 12 and cathode 14 are suitably submerged.

Solution 18 contains copper ions, sulphate ions, a gelatine componentand an active sulphur containing component and means are provided, in amanner that is well known in the art, for applying an electrical currentbetween anode 12 and cathode 14. Thus, copper ions in solution 18 gainelectrons at the peripheral surface 14a of cathode 14 whereby metalliccopper plates out in the form of a foil layer web 20. Cathode 14 rotatescontinuously about its axis 14b during the process and foil layer 20 iscontinuously withdrawn from surface 14a and thus from EPC 10 as acontinuous web which is formed into a roll 20a.

The process depletes the eleotrolyte solution of copper ions, sulphateions, the gelatine component and the active sulphur containingcomponent. And since the process is preferably a continuous processthese ingredients must be continuously replenished. To this end solution18 is withdrawn through line 22 and recirculated through a filter 24, adigester 26 and another filter 28 and then is reintroduced into vessel16 through line 30. Sulphuric acid from a source 32 is fed into digester26 through line 34 and metallic copper from a source 36 is introducedinto digester 26 as indicated schematically along the path 38. Metalliccopper is digested by sulphuric acid to form copper ions in digester 26.

Make-up gelatine component is added to the recirculating solution inline 22 from a source 40 through a line 42. And in accordance with theinvention, the active sulphur containing component is added to therecirculating solution in line 30 through line 44 from a source 46. Thesulphur containing component is preferably introduced into therecirculating solution at a point as near to the vessel 16 as possibleto minimize decomposition of the active sulphur containing component bythe highly acidic recirculating fluid existing from digester 26.

Generally speaking, in commercial applications it is difficult, if notimpossible, to avoid the presence of chloride ions in the electrolytesolution 18. In this regard, it should be noted that chloride ion is acommon contaminant in water and in bulk ingredients. And since thechloride ion concentration has an effect on the properties of theelectroplated foil it is desirable to control the chloride ionconcentration at a known level to eliminate the uncertainties that wouldbe involved if the chloride ion concentration were to fluctuateunpredictably. In the process of the invention it has been determinedthat appropriate results are achieved when the chloride ionconcentration in the electrolyte is in the range of from about 20 toabout 200 ppm, preferably from about 30 to about 100 ppm, and ideallyabout 80 ppm. The chloride ion content in the electrolyte solution maybe controlled by devices that are well known and conventionally employedby those of ordinary skill in the art of production of conductive foilsby electroforming processes.

The concentrations of the active sulphur containing component and thegelatine component in the electrolyte solution may preferably beexpressed in terms of the steady state consumption rate thereof. Theseingredients act at the surface of the copper foil as it forms and areconsumed by the reactions which occur there. And they affect theinternal regions as well as the external surfaces of the foil and thushave a modifying effect on tensile strength, ductility and elongation inaddition to surface roughness.

The consumption rate is determined by the concentration of eachingredient in the electrolyte solution and this is determined by theamount of each ingredient that is added to the electrolyte solutionduring steady state operation. The addition rate may be expressed interms of weight added per unit of time per unit of current flow.Conveniently the addition rate of the active sulphur containingcomponent and of the gelatine component may be defined as milligramsadded to the electrolyte solution per minute per one thousand amperes(mg/min.kA).

The separate roles of ingredients such as the active sulphur containingcomponent and the gelatine component, particularly in electroformingoperations, are discussed in a number of prior literature publicationsand patents. Active sulphur containing components are discussed anddefined in U.S. Pat. No. 2,563,360, the entirety of the disclosure ofwhich is hereby specifically incorporated herein by reference. The '360patent discloses a number of components that contain active sulphur,including thiourea, which are suitable for use in accordance with thepresent invention. For purposes of the invention, however, the preferredcompound is thiourea because it is readily commercially available andrelatively inexpensive and convenient to handle.

Gelatine components are discussed and defined in the E. H. Chia et al.and S. E. Afifi et al. articles cited above. Thus, useful gelatinecomponents are high-protein polymers of amino acids linked by peptidechains, --CO--NH--, and having molecular weights in the range of fromabout 10,000 to 300,000. Commonly animal glue is used as the gelatinecomponent because it is relatively inexpensive, readily commerciallyavailable and convenient to handle.

Thiourea is effectively used as an active sulphur containing additivefor an electrolyte solution that also contains both animal glue as agelatine component and chloride ions and which is used toelectrolytically produce copper foil having uniform controlledroughness. As set forth above, the chloride ion level in the solutionmay preferably be controlled at about 80 ppm. The animal glue itself isoften incapable of effectively producing a desired degree of levelingand smoothness of the deposit and the addition of thiourea produces asubstantial roughness controlling effect. The lowering of the roughnessby the thiourea is thought to occur by a surface adsorption whichaffects the morphology of the growing deposit front. When thiourea,animal glue and chloride ion are simultaneously present in theelectrolyte solution copper foils with a low uniform controlledroughness are produced. It is believed that the glue and chloride maytend to interact with one another to cancel their mutual effects andthus permit the thiourea to have its desired effect.

In accordance with the invention, low profile IPC Class 1 foil mayconveniently be produced. When compared with standard IPC Class 1 foilsproduced without thiourea, the foils produced in accordance with theinvention may have lower roughness, slightly elevated tensile strength,slightly lower elongation characteristics and TD and LD properties thatare more isotropic. In this latter regard, with reference to the foilweb 20 in FIG. 1, TD properties are measured across the web, that is, ina direction parallel to the axis of rotation of cathode drum 14, whileLD properties are measured in a direction along the web. And ifroughness need not be minimized (that is if standard roughness isacceptable) EFC 10 of FIG. 1 may be operated at increased currentdensities to thereby increase the commercial output of the process.

Another unexpected benefit achieved through the use of the invention isthat the tensile strength of the Class 1 foil may be higher and themodulus of elasticity may also be higher than when animal glue alone isused to control roughness. Such foil having higher tensile strength andhigher modulus of elasticity is less susceptible to wrinkling. The netresult of this in a commercial application is that less foil will bedamaged during processing and waste will thereby be reduced.

EXAMPLE I

Initially, experimentation was conducted using a laboratory systemwherein the glue level in the electrolyte solution was maintained atabout 2 ppm at all times. The thiourea concentration in the bathsolution was maintained at about 0, 1, 2 or 3 ppm. The level of chlorideions in the bath solution was maintained at 50 ppm and the cell wasoperated at various cathode current densities ranging from 500 to 1500ASF. 1 oz. copper foil was produced. The results are presented as a bargraph in FIG. 2 and microphotographs of the cross-sections of the fourfoils produced at 1000 ASF are shown in FIGS. 3A through 3D of thedrawings, where 3A shows the cross-section of a foil electrodepositedfrom an electrolyte bath containing 2 ppm animal glue and 0 ppmthiourea; FIG. 3B shows the cross-section of a foil electrodepositedfrom a bath containing 2 ppm animal glue and 1 ppm thiourea; FIG. 3Cshows the cross-section of a foil electrodeposited from a bathcontaining 2 ppm animal glue and 2 ppm thiourea; and FIG. 3D shows thecross-section of a foil electrodeposited from a bath containing 2 ppmanimal glue and 3 ppm thiourea. The leveling power of the thiourea isclearly evident from FIGS. 3A through 3D.

From FIG. 2 it can also be seen that at a 2 ppm concentration of animalglue in the electrolyte bath, the roughness (R_(tm)) decreases as thethiourea concentration is increased.

In known electrodeposition operations, a glue concentration in the orderof 2 ppm is generally used to produce IPC Class 1 foils. The glue levelis increased to reduce roughness and produce low profile foil. And theglue level is decreased to produce IPC Class 3 foils.

In accordance with the present invention, it has been discovered that atglue levels sufficient to produce IPC Class 1 foils, an increase in thelevel of thiourea results in an increase in tensile strength anddecreases in both roughness and elongation. Moreover, it has beendiscovered that in all cases an increase in current density results in adecrease in elongation and increases in both tensile strength androughness. Furthermore, it has been determined that an increase in theglue level results in an increase in tensile strength and decreases inboth roughness and elongation. Additionally, it has been discovered thatat the low glue levels necessary to produce IPC Class 3 foils, theaction of thiourea is inverted and in such case the tensile strength ofthe foil is decreased and the elongation of the foil is increased whenthe thiourea level is increased. This is highly beneficial for purposeof producing a low profile Class 3 foil.

EXAMPLE II

To investigate the production of Class 1 foil using thiourea inaccordance with the invention, a number of test runs were conductedusing a production scale electroforming system set up as illustrated inFIG. 1. In all these tests EFC 10 was operated at a current density of460 amps per square foot of active cathode surface (ASF), glue was addedthrough line 42 at rates of 15.12 mg/min.kA or 9.0 mg/min.kA andthiourea was added through line 44 at rates ranging from 0 to 30mg/min.kA. In each case a 1 oz. foil was produced In connection withthese tests it was discovered that a 9.0 mg/min kA addition rate isappropriate to maintain a bath concentration of roughly about 2 ppm andit is believed that the bath concentration of each additive variesdirectly with addition rates; however, there is no good method foraccurately measuring the concentration of a given component in the bathat any particular moment in time. Accordingly, these correlations, whilebelieved to be appropriate, may not always be completely accurate. Thedata collected from these tests are set forth in Table 2.

                                      TABLE 2                                     __________________________________________________________________________       Glue   Thiourea     Room      Room                                            Addition                                                                             Addition                                                                             Roughness                                                                           temperature (LD)                                                                        temperature (TD)                             Run                                                                              Rate   Rate   (R.sub.tm)                                                                          characteristics*                                                                        characteristics*                             No.                                                                              mg/min · kA                                                                 mg/min · kA                                                                 μm T.S. (psi)                                                                         % Elong                                                                            T.S. (psi)                                                                         % Elong                                 __________________________________________________________________________    2-1                                                                              15.12  0      5.9   57,210                                                                             12.63                                                                              56,830                                                                             11.79                                   2-2                                                                              15.12  20     4.3   58,140                                                                             10.95                                                                              58,030                                                                              8.78                                   2-3                                                                              15.12  30     3.4   62,950                                                                             14.19                                                                              62,150                                                                             13.95                                   2-4                                                                              9      0      7.8   49,300                                                                             16.13                                                                              47,410                                                                             12.07                                   2-5                                                                              9      0      7.2   46,230                                                                             12.50                                                                              44,100                                                                              8.71                                   2-6                                                                              9      10     7.6   35,460                                                                             10.13                                                                              36,310                                                                             11.25                                   2-7                                                                              9      25     3.5   68,820                                                                             12.67                                                                              69,850                                                                             10.55                                   __________________________________________________________________________     *Tensile strength and ductility characteristics are determined as             specified in IPCCF-150E                                                  

From Table 2 it can be seen that the tensile strength and elongationcharacteristics of each foil is well above the minimum values set forthin Table 1 above for IPC Class 1 foil. Moreover, the roughnesses arequite low and in the case of runs 2-2, 2-3 and 2-7 are as low as typicalshiny side roughnesses (R_(tm)) which range from about 3.5 to about 4.5μm, and are lower than for raw 1 oz. IPC Class 1 low profile foilproduced using only glue as a leveler which typically has an R_(tm)roughness in the order of about 5.2 μm.

Thus, IPC Class 1 low profile foil may be produced, in accordance withthe invention, without the need for decreasing current densities andwithout loss of metallurgical properties.

Additionally, since the roughness is initially so low and the elongationis so high current density may be increased to increase production. Insuch case the roughness will increase and the elongation may decrease;however, much greater production rates are achievable while stillproducing a acceptable Class 1 foil. An added benefit is that thealready high tensile strength will be increased as the current densityincreases and the foil will thus achieve enhanced resistance towrinkling.

In sum, for production of IPC Class 1 foils, the addition of thiourea tothe electrolytic cell solution provides three separate and distinctadvantages:

1. R_(tm) roughness may be decreased to provide a Class 1 low profilefoil;

2. Tensile strength may be increased and the modulus of elasticity alsoincreased to provide a wrinkle resistant Class 1 foil; and

3. Higher current density may be used to increase production withoutconcomitant loss of Class 1 properties.

EXAMPLE III

In this example a number of test runs were conducted using a productionscale electroforming cell to investigate the production of IPC Class 3foils using thiourea as an electrolytic bath solution additive. Thetests were conducted using an EFC 10 as illustrated in FIG. 1. In eachof these tests a 2 oz. foil was deposited. The current density wasvaried from 825 to 1100 ASF, the glue addition rate was varied from 0.3mg/min.kA to 0.6 mg/min kA and the thiourea addition rate was variedbetween 0 and 5.0 mg/min.kA. The data collected are set forth in Table3.

                                      TABLE 3                                     __________________________________________________________________________            Glue   Thiourea     Room      180° Elevated                       Current                                                                            Addition                                                                             Addition                                                                             Roughness                                                                           temperature (LD)                                                                        temperature (TD)                        Run                                                                              Density                                                                            Rate   Rate   (R.sub.tm)                                                                          characteristics*                                                                        characteristics*                        No.                                                                              ASF  mg/min · kA                                                                 mg/min · kA                                                                 μm T.S. (psi)                                                                         % Elong                                                                            T.S. (psi)                                                                         % Elong                            __________________________________________________________________________    3-1                                                                              825  0.3    0      14.74 50,450                                                                             25.36                                                                              30,630                                                                             6.03                               3-2                                                                              825  0.3    5      11.17 39,460                                                                             35.60                                                                              23,630                                                                             14.02                              3-3                                                                              917  0.3    4.5    10.08 40,050                                                                             35.89                                                                              22,690                                                                             12.36                              3-4                                                                              917  0.3    4.5    10.97 40,680                                                                             35.91                                                                              22,720                                                                             12.32                              3-5                                                                              917  0.3    4.05   11.07 40,910                                                                             36.24                                                                              22,590                                                                             11.51                              3-6                                                                              1100 0.3    3.38   11.84 44,610                                                                             30.03                                                                              26,180                                                                             9.42                               3-7                                                                              1100 0.3    3.38   12.34 44,490                                                                             30.89                                                                              23,880                                                                             9.20                               3-8                                                                              1100 0.3    1.69   14.28 42,290                                                                             32.20                                                                              23,310                                                                             10.42                              3-9                                                                              917  0.3    2.03   13.32 39,480                                                                             36.70                                                                              21,370                                                                             12.31                              3-10                                                                             917  0.4    4.05   11.56 38,790                                                                             35.48                                                                              23,990                                                                             15.97                              3-11                                                                             917  0.6    3.5    11.04 38,290                                                                             36.55                                                                              22,950                                                                             12.72                              3-12                                                                             917  0.6    3.5    11.09 41,190                                                                             35.80                                                                              22,430                                                                             12.93                              3-13                                                                             917  0.6    3.5    10.51 40,290                                                                             36.94                                                                              22,870                                                                             9.74                               3-14                                                                             1100 0.6    3.38   13.14 44,230                                                                             31.49                                                                              25,560                                                                             5.23                               3-15                                                                             917  0.6    0      16.67 49,320                                                                             24.23                                                                              29,490                                                                             4.83                               __________________________________________________________________________     *Tensile strength and ductility characteristics are determined as             specified in IPCCF-150E                                                  

EXAMPLE IV

In this example a number of test runs were conducted using a productionscale electroforming cell. Again the system was set up like the systemof FIG. 1. The tests were designed to produce IPC Class 3 foil usingthiourea as a bath additive. In each of these tests the glue additionrate was 0.53 mg/min.kA and a 2 oz. foil was electrodeposited. Thecurrent density was either 733 ASF or 1100 ASF and the thiourea additionrate was varied between 0 and 30 mg/min.kA. The data collected are setforth in Table 4.

                  TABLE 4                                                         ______________________________________                                                      Thiourea           Room                                              Current  Addition   Roughness                                                                             temperature (TD)                             Run  Density  Rate       (R.sub.tm)                                                                            characteristics*                             No.  ASF      mg/min · kA                                                                     μm   T.S. (psi)                                                                           % Elong                               ______________________________________                                        4-1   733     0          14.49   30,220 5.80                                  4-2  1100     0          too rough                                                                             29,720 4.80                                                           to measure                                           4-3   733     9.3         8.59   24,140 13.83                                 4-4   733     9.3         8.96   23,980 13.15                                 4-5   733     27.9        9.38   24,010 11.75                                 4-6   733     27.9       10.37   25,350 10.52                                 4-7  1100     10         11.28   29,060 3.86                                  4-8  1100     10         12.18   29,150 4.55                                  4-9  1100     30          9.46   29,440 5.96                                   4-10                                                                              1100     30          9.39   30,750 6.39                                   4-11                                                                              1100     10         13.27   26,250 3.22                                  ______________________________________                                         *Tensile strength and ductility characteristics are determined as             specified in IPCCF-150E                                                  

With reference to Tables 3 and 4 it can be seen that the tensilestrength and elongation characteristics of each foil is well above theminimum values set forth in the IPC Table presented above for Class 3foils. Moreover, the roughnesses of the foils produced with thioureaadded to the electrolyte solution are much lower than the roughnesses ofthe foils produced without thiourea addition. With reference to Tables 3and 4 it can be seen when thiourea is added to the electrolyte solutionClass 3 foils are produced at high current densities.

For production of IPC Class 3 foils, the addition of thiourea to theelectrolytic cell solution offers three separate and distinctadvantages:

1. R_(tm) roughness may be decreased to provide a Class 3 low profilefoil;

2. Elongation may be increased to provide an improved Class 3 foil; and

3. Higher current density may be used to increase production withoutconcomitant loss of Class 3 properties.

As a preferred embodiment, IPC Class 3 2 oz. foil may be produced in anEFC 10 as depicted in FIG. 1 as follows:

    ______________________________________                                        Current Density:    1100 ASF                                                  Glue Rate:          0.35 mg/min · kA                                 Thiourea Rate:      5 mg/min · kA                                    R.sub.tm Roughness: 11 to 12 μm                                            180° Tensile Strength:                                                                     28,000 to 30,000 psi                                      180° Elongation:                                                                           4 to 6%                                                   ______________________________________                                    

We claim:
 1. A process for electrolytically forming copper foil for usein printed circuit board applications comprising:A) providing anelectrolyte solution containing copper ions and sulfate ions whereinsaid electrolyte solution has immersed therein an anode and a cathode;B) continuously supplying to said electrolyte solution a quantity of agelatin component consisting essentially of high-protein polymers ofamino acids linked by peptide chains having molecular weights in therange of from about 10,000 to about 300,000 and a quantity of an activesulfur containing component having a bivalent sulfur atom wherein bothbonds of which are directly connected to a carbon atom together with oneor more nitrogen atoms also directly connected to the carbon atomwherein said quantities are sufficient to produce an IPC-CF-150E Class 1copper foil; and C) applying a voltage across said anode and cathodeimmersed in said electrolyte solution to thereby cause theelectrodeposition of a Class 1 copper foil at said cathode.
 2. A processfor electrolytically forming copper foil for use in printed circuitboard applications comprising:A) providing an electrolyte solutioncontaining copper ions and sulfate ions wherein said electrolytesolution has immersed therein an anode and a cathode; B) continuouslysupplying to said electrolyte solution a quantity of a gelatin componentconsisting essentially of high-protein polymers of amino acids linked bypeptide chains having molecular weights in the range of from about10,000 to about 300,000 and a quantity of an active sulfur containingcomponent having a bivalent sulfur atom wherein both bonds of which aredirectly connected to a carbon atom together with one or more nitrogenatoms also directly connected to the carbon atom wherein said quantitiesare sufficient to produce an IPC-CF-150E Class 3 copper foil; and C)applying a voltage across said anode and cathode immersed in saidelectrolyte solution to thereby cause the electrodeposition of a Class 3copper foil at said cathode.
 3. The process as set forth in claim 1,wherein said quantity of said active sulphur containing component issufficient for decreasing the roughness of a 1 oz. electrodepositedcopper foil to an R_(tm) of less than about 5.0.
 4. The process as setforth in claim 1, wherein said quantity of said active sulphurcontaining component is sufficient for increasing the tensile strengthof the electrodeposited foil.
 5. The process as set forth in claim 1,wherein said quantity of said active sulphur containing component issufficient to enable increasing the current for electrolytically formingsaid copper foil to greater than about 500 ASF without substantiallyaltering the basic characteristics of the foil.
 6. The process as setforth in claim 5, wherein said quantity of said active sulphurcontaining component is sufficient to enable increasing said currentfrom about 500 ASF to about 1500 ASF without substantially altering thebasic characteristics of the foil.
 7. The process as set forth in claim2, wherein said quantity of gelatine component is present in an amountsufficient to facilitate the production of an IPC Class 3 foil and saidquantity of said active sulphur containing component is sufficient fordecreasing the roughness of a 1 oz. electrodeposited IPC Class 3 foil toan R_(tm) of less than about 7.0.
 8. The process as set forth in claim7, wherein said quantity of said gelatine component is present in anamount sufficient to facilitate the production of an IPC Class 3 foiland said quantity of said active sulphur containing component issufficient to enable increasing the current for electrolytically formingsaid copper foil to greater than about 500 ASF without substantiallyaltering the basic Class 3 characteristics of the foil.
 9. The processas set forth in claim 8, wherein said quantity of said active sulphurcontaining component is sufficient to enable increasing said currentfrom about 500 ASF to about 1500 ASF without substantially altering thebasic characteristics of the foil.
 10. The process as set forth in claim1, wherein said gelatine component comprises animal glue.
 11. Theprocess as set forth in claim 10, wherein said active sulphur containingcomponent comprises thiourea.
 12. The process as set forth in claim 11,wherein said animal glue is added to said solution at a rate in therange of from about 0.2 mg/min.kA to about 20 mg/min.kA and saidthiourea is added to said solution at a rate in the range of from about1.25 mg/min.kA to about 50 mg/min.kA.
 13. The process as set forth inclaim 11, wherein said animal glue is added to said solution at a ratein the range of from about 5 mg/min.kA to about 20 mg/min.kA and saidthiourea is added to said solution at a rate in the range of from about10 mg/min.kA to about 50 mg/min.kA.
 14. The process as set forth inclaim 11, wherein said animal glue is added to said solution at a ratein the range of from about 8 mg/min.kA to about 10 mg/min.kA and saidthiourea is added to said solution at a rate in the range of from about20 mg/min.kA to about 30 mg/min.kA.
 15. The process as set forth inclaim 2, wherein said gelatine component is animal glue and is added tosaid solution at a rate less than about 5 mg/min.kA and said activesulfur component is thiourea and is added to said solution at a rateless than about 10 mg/min.kA.
 16. The process as set forth in claim 15,wherein said animal glue is added to said solution at a rate of about0.3 mg/min.kA and said thiourea is added to said solution at a rate ofabout 5 mg/min.kA.
 17. An electrolytic bath for electrodepositing copperfoil for printed circuit board applications comprising an aqueoussolution containing copper ions, sulphate ions, a quantity of a gelatinecomponent consisting essentially of high protein polymers of amino acidslinked by peptide chains having molecular weights in the range of fromabout 10,000 to about 300,000 and a roughness decreasing quantity of anactive sulphur containing component having a bivalent sulfur atomwherein both bonds of which are directly connected to a carbon atomtogether with one or more nitrogen atoms also connected to the carbonatom wherein said quantities are sufficient to produce an IPC-CF-150EClass 1 or Class 3 copper foil.
 18. An electrolytic bath as set forth inclaim 17, wherein said active sulphur containing component is thiourea.19. An electrolytic bath as set forth in claim 17, wherein said gelatinecomponent is animal glue.
 20. An electrolytic bath as set forth in claim19, wherein said animal glue is present in an amount ranging from about0.044 ppm to about 4.4 ppm.
 21. An electrolytic bath as set forth inclaim 18, wherein said quantity of thiourea present in said bath rangesfrom about 0.28 ppm to about 11.1 ppm.
 22. A 2 oz. copper foil as setforth in claim 17 having a tensile strength of at least 25,000 psi andan elongation of greater than 5% as measured at 180° C.
 23. A copperfoil as set forth in claim 17, wherein said foil is electrolyticallydeposited at a current density of 1100 ASF.
 24. A copper foil as setforth in claim 17 having a tensile strength of at least 65,000 psi andan elongation of greater than 12% as measured at room temperature.
 25. A2 oz. copper foil for printed circuit board applications havingIPC-CF-150E Class 1 properties and an R_(tm) of less than about 8.0 μm.26. A 1 oz. copper foil for printed circuit applications havingIPC-CF-150E Class 1 properties and an R_(tm) of less than about 5 μm.27. A 1/2 oz. copper foil for printed circuit board applications havingIPC-CF-150E Class 1 properties and an R_(tm) of less than about 4.6 μm.28. A low profile copper foil for printed circuit board applicationshaving IPC-CF-150E Class 3 properties.
 29. A 2 oz. copper foil forprinted circuit board applications having IPC-CF-150E Class 3 propertiesand an R_(tm) of less than about 11 μm.
 30. A 1 oz. copper foil forprinted circuit board applications having IPC-CF-150E Class 3 propertiesand an R_(tm) of less than about 7 μm.
 31. A 1/2 oz. copper foil forprinted circuit board applications having IPC-CF-150E Class 3 propertiesand an R_(tm) of less than about 5 μm.